Method for making cold-process bituminous mix

ABSTRACT

The invention concerns a method for making cold-process bituminous mixes, using a bitumen-type emulsion in aqueous phase and aggregates. It consists in treating said aggregates with an agent providing hydrophobicity, prior to mixing said emulsion with said aggregates.

[0001] This disclosure is based upon, and claims priority from, Frenchpatent application No. 13519 filed Oct. 23, 2000, the contents of whichare incorporated by reference herein

[0002] The present invention concerns making cold-process bituminousmix, usable in particular in the paving industry, using a bitumen-typeemulsion in aqueous phase mixed with aggregates.

[0003] In paving technology, bituminous mixes are materials used in theconstruction and maintenance of paving systems and their surfaces, andfor road repair work. They are composed of mineral aggregates, mostly ofsiliceous nature (flint, quartzite, granite) or silica-calcium, andbituminous binders.

[0004] According to the aggregate coating method, these mixes areclassified in two categories: hot coating, prepared with materials, witha bituminous type binder, that are raised to relatively hightemperatures, and cold coating, achieved by emulsifying the binder inliquid phase with a surfactant, using the mechanical energy (cementmixer, turbine) needed for the dispersion of the binder in finedroplets, and blending with the aggregates at lower temperatures.

[0005] From the environmental perspective, cold-process mixes have theimportant advantage that, during their implementation, they do notproduce the emission of fumes, and are therefore quite suitable forurban roadways. They also have great flexibility of use because of thelow temperatures required for their application, particularly inlocations where it is not possible to have a heating device. During theapplication of the cold-process composition in paving construction, thebreakdown of the emulsion occurs, with elimination of the water and theformation of a continuous adhesive film of the bitumen-type binder onthe aggregates.

[0006] Emulsions have been used in paving technology for many years andhave been constantly improved. The resurgence of interest incold-process mixing techniques and their new spectrum of application,particularly for paving materials suitable for heavy traffic highways,have led to a better understanding, on the one hand, of the mechanismsof breakdown of the emulsion between the mixing stage, particularly theblending type, and the steps of spreading and compacting, in order topreserve a workability of the mixture compatible with its use,particularly during storage and transport, and on the other hand, themechanisms of film formation of the emulsion on the aggregates.

[0007] The film formation of the bitumen around the aggregates involvesfour successive steps, the kinetics of which must be controlled:

[0008] the wetting of all the minerals by the emulsion,

[0009] the heteroflocculation of the droplets of bitumen, whichestablishes the distribution of the bitumen on the mineral surface andwhich is essential with respect to the continuity of the film,

[0010] the coalescence of the droplets of bitumen, which is the step ofdestabilization of the emulsion,

[0011] the maturation of the bitumen, corresponding to the molecularrearrangement within the bitumen, which is essential to achieving withina short time, if possible during compacting, the optimal mechanicalperformances including cohesion.

[0012] With cationic emulsions, the use of aggregates that arepredominantly calcareous sometimes results in problems of adherence ofthe bitumen. This is explained by the formation of a friable layer dueto the attack of the surface of the aggregate by HCI, and by theexcessively quick breakdown of the emulsion following an abrupt increaseof the pH.

[0013] Moreover, the coalescence should develop progressively in orderto give the mix a satisfactory period of workability, while stillpreserving the ability to develop a strong final cohesion.

[0014] An attempt to improve the workability was approached in thepatent FR 2,695,664, which describes a method of obtaining densecold-process mixes, by coating aggregates with an emulsion mixed with ahard bitumen and a soft bitumen, in proportions such that their mixturehad the desired final hardness. However, this document does not offerany solution to controlling the speed of breakdown of the emulsion andis not concerned with the evolution of interface phenomena of theaggregates/emulsion system.

[0015] Another approach is described in the application EP 896,985,which concerns a method of producing dense mixtures by coatingaggregates with a bituminous emulsion comprised of a mixture of aslow-breakdown emulsion and a fast-breakdown emulsion. Unfortunately,this method of producing mixtures requires the use of two emulsions andis therefore more restrictive than the usual method. In addition, it isnot concerned with the hydrophobation of the aggregates, and thecoalescence kinetics of the bitumen that conditions the rapid increasein cohesion of the mix is not controlled.

[0016] Furthermore, the control of the moment of breakdown of an aqueousemulsion of bitumen is described in patent EP 864,611, by theincorporation of an encapsulated breakdown agent, which is released bymechanical action during the compacting. Unfortunately, this method doesnot allow the interactions between aggregates and emulsion to be limitedduring the period prior to the compacting.

[0017] The Applicant has carried out research that has allowed her tomake progress in understanding the breakdown phenomena and themechanisms governing the film formation of the cold-process mixes,particularly due to the characterization of the interface properties andof the molecular structure of the surfactants used by molecularmodeling.

[0018] In particular, she has established that, surprisingly, thehydrophobation of all of the mineral surface of the aggregates, beforemixing them with the emulsion, by considerably limiting the interactionswith the emulsion and therefore the possibilities of breakdown thereof,gives the mix an increased workability from the coating stage to thespreading stage. This hydrophobation is obtained through the use of anappropriate interface agent or dope, composed of polar organic moleculesthe adsorption of which on the aggregates forms a hydrophobic film, thusmodifying the surface condition. This film should preferably be formedas a single layer on the aggregates. The rate of hydrophobation obtainedmakes it possible to act on the coalescence kinetics and therefore onthe speed of breakdown of the emulsion. Moreover, the hydrophobationallows the subsequent coating of the aggregates by the bitumen,irrespective of the nature of said aggregates.

[0019] An object of the invention, therefore, is a method for makingcold-process bituminous mix, using a bitumen-type emulsion in aqueousphase and aggregates, characterized in that prior to mixing the emulsionwith said aggregates, they are treated with a hydrophobation agent.

[0020] According to the invention, the hydrophobation agent acts as amodifier of the surface tension of the surface of the aggregates.

[0021] In particular, the molecules of the hydrophobation agent form anorganic lipophilic film on the surface of the aggregates.

[0022] Preferably, the hydrophobation agent is composed of amino acid oralkylamine compounds.

[0023] Other compounds, such as those of the water repellent type, ormacromolecular surfactant compounds, can also be used.

[0024] In particular, the amino acid compounds can bepolyalkylamphopolycarboxyglycinates, and especiallytallow-amphopolycarboxyglycinates.

[0025] Furthermore, the alkylamine compounds can bealkylsulfpolypropylenepolyamines.

[0026] Also, the hydrophobation agent for the aggregates can be composedof polyoxyethylenepolyalkyletherphosphate, such as polyoxyethylene oleyletherphosphate.

[0027] More particularly, the hydrophobation agent is used in liquidphase, during the wetting of the aggregates, and preferably in aqueousphase.

[0028] In a preferred form of embodiment, the hydrophobation surfactantis introduced at a rate of at least 0.04% by weight with reference tothe aggregates.

[0029] According to the invention, the bitumen type emulsion is producedfrom natural bitumen, which is selected from among pure bitumens, fluxedbitumens, and bitumen modified by polymers, and which is dispersed inaqueous phase with an emulsifying agent. Natural bitumen is understoodas being the product obtained particularly as the residue fromdistillation under vacuum of crude oil and the extraction of asphaltfrom this residue.

[0030] Advantageously, the bitumen is a hard grade 50/70 (penetrabilityat 25° C., measured according to the standard NF The 66-004), which canbe acidified in particular by a fatty acid pitch.

[0031] The emulsion can also be produced from synthetic binder.

[0032] Preferably the bituminous emulsion includes between 60% and 70%by weight of bitumen.

[0033] In the method according to the invention, between the step ofmixing the emulsion and the aggregates and the step of application byspreading the mixture thus obtained, the duration of workability is morethan four hours, preferably at least eight hours, and still morepreferably, at least 24 hours.

[0034] The Applicant has also established that after the mixture isspread, the mechanical energy used for the compacting, which is anessential step for the densification of the mix, is not enough to causethe complete breakdown of the emulsion, so that this breakdown canadvantageously be obtained by adding a coalescence agent to theemulsion. The molecules of the coalescence agent, by modifying thehydrophilic-lipophilic balance at the interface of the phases of thesurfactant of the emulsion, cause the breakdown of the water-bitumeninterface films and the agglomeration of the droplets in “clusters” onthe aggregates. This step contributes to improving the speed ofintensification of cohesion of the mix and its resistance todisintegration by water.

[0035] The method according to the invention, therefore, encompasses theintroduction into the bitumen type emulsion of a coalescence agent.

[0036] According to the invention, the coalescence agent is composed ofC12 to C14 ethoxylated and propyloxylated amines, C8 to C12 ethoxylatedand glycolic alcohols or antifoaming type compounds such as C20 to C30mineral oils with ethoxylated silicon sites or mixtures of silicon oilsand silica.

[0037] Preferably, the coalescence agent is introduced at the rate of atleast 0.03% by weight with reference to the aggregates, immediatelybefore mixing them with the emulsion. This coalescence agent isintroduced into the bituminous emulsion preferably in aqueous phase.

[0038] According to the invention, the cold-process bituminous mixcomposition also includes the introduction of a film-forming agent intothe bitumen type emulsion.

[0039] In effect, the coalescence of the droplets of bitumen isaccompanied by a contraction in volume, corresponding to a more stablethermodynamic equilibrium (formation of clusters), and the action of afilm-forming agent becomes necessary to obtain a continuous film ofbitumen, which results in better cohesion of the mixture.

[0040] More particularly, the film-forming agent can be composed ofalkyl polyacrylate, and in particular, ethyl polyacrylate. In apreferred mode of embodiment, it is introduced at a rate of at least0.12% by weight with reference to the aggregates, prior to mixing.However, the coalescence agent and the film-forming agent can also beintroduced after mixing.

[0041] The bituminous emulsion is obtained by introducing into the watera common emulsifier or surfactant, such as alkylamine derivatives,mixtures of alkylamidopolyamines and quaternary ammonium salts, oralklypropylenepolyamine compounds such as N tallow-propylenepolyamines.

[0042] This type of emulsion is cationic, but it is obvious that theinvention also applies to anionic or non-ionic emulsions.

[0043] The cold-process bituminous mix composition according to theinvention has particularly advantageous application in the pavingindustry, especially as dense mixes, drainage mixes, thin bitumenconcretes (BBM), very thin bitumen concretes (BBTM), ultra-thin bitumenconcretes (BBUM), and cold-poured mixes, for construction of underlaysor pavement.

[0044] However, other industrial applications can be considered.

[0045] Preferred methods of implementation of the invention will now bedescribed.

[0046] To make cold-process bituminous mixes according to the invention,different formulations of cold-process mixes are made (with compactnessof more than 90%), by using aggregates of the Meilleraie type (siliceousporphyric diorites, which can be assimilated in a mixture of SiO₂/CaO60/40% by weight), with grain size of 0/10.

[0047] 1. Hydrophobation of the Aggregates

[0048] They are hydrophobic the moment they are wetted by an amino acidtype additive, which is a tallow-amphopolycarboxyglycinate.

[0049] The adsorption of this additive on the aggregates has beenexamined by determining the surface tensions of the aqueous phasesrecovered by centrifuging, after the wetting solution has been incontact with the aggregates for one hour. The measurements of surfacetension were made with a plate tensiometer at an average temperature of20° C., but it is possible to use another type of device such as apendant drop tensiometer.

[0050] The line of the curve of the surface tension as a function of theconcentration of hydrophobation agent shows a plateau up to aconcentration of about 0.04% by weight with reference to the aggregates.Beyond that there is a rapid decrease of this surface tension due to theexcessive presence of this agent in the aqueous phase. This limitconcentration corresponds to the adsorption of a single layer of thehydrophobation agent, and it is used as the optimal value. In practice,the aggregates are treated with 4 pph (parts per hundred) of an aqueoussolution of 1% by weight of this hydrophobation agent.

[0051] The hydrophobation agent, however, can also be an alkylaminecompound such as a derivative of tallow-dipropylene triamine, or apolyoxyethylenepolyalkyleterphosphate.

[0052] 2. Producing Formulations of Mixes

[0053] The bitumen used is a Viatotal 50/70 bitumen from TOTALFINAELF,acidified by a fatty acid pitch, the cationic emulsion of which, at aconcentration of 60% by weight, is done with the emulsifier marketed byCECA under the name Stabiram 730, which is a mixture ofalkylamidopolyamines and quaternary ammonium salts (10 kg/ton ofemulsion) with hydrochloric acid (5.4 kg/ton of emulsion). Of course,the bitumen can be acidified by other products.

[0054] A first formulation 1 was produced with a hot-process mix forreference. A second comparative formulation 2 was produced with theabove emulsion without introducing a coalescence agent and film-formingagent, and with the aggregates made hydrophobic as above.

[0055] Various additives are then incorporated into the bituminousemulsion in order to obtain, after coating the aggregates in a blender,the following compositions:

[0056] formulation 3: introduction, immediately prior to the coating ofthe aggregates in the preceding emulsion, of a coalescence agent Acomposed of C20 to 30 mineral oil with silicone ethoxyl sites,introduced at the rate of 2 pph (parts per 100 parts of aggregates) of asolution at 1.5% by weight;

[0057] formulation 4: introduction of a coalescence agent/film-formingagent pair, comprised of the product A as mentioned above and at thesame rate, and as film-forming agent, a compound B, which is an aqueoussolution of ethyl polyacrylate, at the rate of 2% by weight withreference to the bitumen;

[0058] formulation 5: introduction of a coalescence agent/film-formingagent pair, comprised of the compound C, an anionic compound ofethoxylated and propyloxylated amines from C12 to C14, at the same rateas the product A, and the product B, at the same rate as before.

[0059] The coating of the aggregates is carried out so as to obtain aresidual concentration of bitumen of 6.2 pph (parts per 100 parts ofaggregates).

[0060] Different characteristics of the different formulations ofcold-process mixes are measured, to wit:

[0061] the percentage by weight of water lost during compacting, and thepercentage by weight of water lost after 24 hours at 20° C., measuredduring the production of test specimens from mixes according to theDURIEZ test described in the standard NF P 98-251-1;

[0062] the passive adhesive force according to NFT 66 018;

[0063] the compressive strength under different conditions, measuredaccording to the DURIEZ test described in the standard NF P 98-251-1,which specifies a test method the purpose of which is to determine, fora given temperature and compaction, the water content of ahydrocarbonated mix, from the ratio r₁/R₂ or I/C of compressivestrengths with and without immersion of coated test samples (r₁designating the compressive strength measured after 7 days at 18° C. inwater and R₂ designating the compressive strength measured after 7 daysat 18° C. with 50% relative hydrometry RH).

[0064] The results are shown in the following Table. Formulations 1 2 34 5 Coalescence agent — — A A C Film-forming agent — — — B B % by weightof water lost during — 49 65 72 69 compaction % by weight of water lostafter 24 hrs — 63 84 80 86 at 20° C. without ventilation Passiveadhesiveness per NFT 66 018 90 90 90 90 90-100 Compressive strength perNFP — 3.4 4.5 5.8 5.1 98-251-1 in MPa R₁, 1 day at ambient temperatureR₂ 8 days, 7 days of which at 8.0 6.4 7.8 8.0 7.2 18° C. 50% RH r₁ 8days, 7 days of which at 8.0 3.3 4.8 5.9 5.8 18° C. in water I/C = r₁/R₂1.0 0.52 0.62 0.74 0.80

[0065] By comparing the percentages of water lost during the compactingof the formulations of mixes without the coalescence agent (No. 2) andwith this agent (Nos. 3-5), the effectiveness of this additive for thedrainage of water from the emulsion is obvious (increase of more than30% of the weight of water eliminated).

[0066] Moreover, it can be seen from the compressive strength valuesobtained, measured at 1 and 8 days after compaction, that at the mix,the introduction of the hydrophobation agent of the aggregates(formulation 2) makes it possible to obtain values of cohesion that arealready appreciable, while with the same emulsion but withouthydrophobation of the aggregates, it is not possible to produce testsamples to run this test, following an immediate breakdown of theemulsion and caking of the aggregates.

[0067] Furthermore, on the one hand the introduction of a coalescenceagent, and on the other hand a coalescence agent/film-forming agent pairin the formulations of mixes, has a positive effect on their speed ofincrease of cohesion, on their final mechanical strength, as well as ontheir water content (I/C).

[0068] In particular it is with the C/B that the best water content ofthe mix (I/C=0.80) is obtained, which is quite satisfactory compared tothe reference hot-process mix (I/C=1) and compared to the value of theNFP 98-130 hot mix standard which gives I/C≧0.75.

[0069] These good performances are confirmed by the value of passiveadhesiveness according to NFT 66 018, which is 90-100.

[0070] The mixes according to the invention have a satisfactoryworkability, can be stored and handled prior to compacting for a periodof at least 24 hours after mixing of the aggregates with a bituminousemulsion, even when using a fast breakdown emulsion of the type used forsurface coatings, while mixes produced with the same aggregatesuntreated lose, upon mixing of the aggregates and the bitumen emulsion,all handling and storage properties after the very quick breakdown ofthe emulsion, well before compacting.

1: Method for making cold-process bituminous mix, using a bitumenemulsion in aqueous phase and aggregates, characterized in that prior tomixing the emulsion with said aggregates, they are treated with ahydrophobation agent. 2: Method according to claim 1, characterized inthat the hydrophobation agent is selected from among compounds suitablefor modifying the surface tension of the surface of the aggregates. 3:Method according to claim 2, characterized in that the hydrophobationagent is selected from among compounds the molecules of which aresuitable for forming a lipophilic organic film on the surface of theaggregates. 4: Method according to any one of claims 1 to 3,characterized in that the hydrophobation agent is composed of amino acidcompounds. 5: Method according to any one of claims 1 to 3,characterized in that the hydrophobation agent is composed ofalkylamines. 6: Method according to any one of claims 1 to 3,characterized in that the hydrophobation agent is a macromolecular typesurfactant. 7: Method according to claim 4, characterized in that theamino acid compounds are polyalkylamphopolycarboxyglycinates. 8: Methodaccording to claim 7, characterized in that the amino acid compounds aretallow-amphopolypropylenepolyamines. 9: Method according to claim 5,characterized in that the alkylamine compounds arealkyl-tallow-polypropylenepolyamines. 10: Method according to any one ofclaims 1-3, characterized in that the hydrophobation agent is used inliquid phase, during the wetting of the aggregates. 11: Method accordingto any one of claims 1-3, characterized in that the bitumen emulsion isproduced from natural bitumen, selected from among pure bitumens, fluxedbitumens, and modified bitumens and dispersed in aqueous phase with anemulsifying agent. 12: Method according to any one of claims 1-3,characterized in that the bitumen emulsion is produced from syntheticbinder. 13: Method according to any one of claims 1-3, characterized inthat the bitumen emulsion includes between 60% and 70% by weight ofbitumen. 14: Method according to any one of claims 1-3, characterized inthat the bitumen emulsion also includes a coalescence agent. 15: Methodaccording to claim 14, characterized in that the coalescence agent isselected from the group consisting of C12 to C14 ethoxylated andpropyloxylated amines, C8 to C12 ethoxylated and glycolic alcohols, andantifoaming compounds. 16: Method according to claim 15, characterizedin that the coalescence agent is introduced into the emulsionimmediately prior to mixing it with the aggregates. 17: Method accordingto any one of claims 1-3, characterized in that the bitumen emulsionalso includes a film-forming agent. 18: Method according to claim 17,characterized in that the film-forming agent is composed of an alkylpolyacrylate. 19: Method according to claim 18, characterized in thatthe film-forming agent is introduced into the emulsion immediately priorto mixing it with the aggregates. 20: A method of constructing underlaysor pavement, comprising producing dense mixes, draining mixes, thinbituminous concretes (BBM), very thin bituminous concretes (BBTM),ultra-thin bituminous concretes (BBUM), or cold-poured mixes from thecold-process bituminous mix obtained by the method according to any ofclaims 1-3. 21: Method according to claim 15, characterized in that thecoalescence agent is an antifoaming compound, and the antifoamingcompound is a C20 to C30 mineral oil with ethoxylated silicon sites or amixture of silicon oil and silica. 22: Method according to claim 18,characterized in that the alkyl polyacrylate is an ethyl polyacrylate.